234-5 Deformation in Dhaka Induced by Changing Water Levels Above and Below the Ground Surface

Session: Advance Ground Surface Modeling for Hydrological and Environmental Applications

Presenting Author:

Cameron deFabry

Authors:

deFabry, Cameron Mark¹, Chen, Jingyi 'Ann'², Ahmed, Kazi Matin Uddin³, Khan, Mahfuzur Rahman⁴, Knappett, Peter Shawn Kuehl⁵, Cardenas, Meinhard Bayani R⁶

Abstract:

Dhaka, the capital of Bangladesh and home to 20 million people is a largely groundwater dependent city with the deep aquifer (>150 m) providing potable water quality . Groundwater pumping here has caused a >70-meter head drop causing aquifer/aquitard compaction and subsidence . Groundwater pumping has been correlated to increasing aqueous arsenic (As) concentrations due to multiple physical and chemical processes that likely occur simultaneously. Given that Interferometric Synthetic Aperture Radar (InSAR) surface deformation analysis can be used to monitor groundwater aquifers at a much finer spatial resolution than traditional hydrographs alone, this study seeks to better understand and explain the connections between groundwater pumping and associated aquifer/aquitard compaction with InSAR observations. However, a complication in the surface deformation of Dhaka has been found as the South Asian monsoon can inundate the region with a meter level rise of water, also causing surface deformation. As such, this study further seeks to explain the connections between surface deformation, and flooding. Ninety-eight Sentinel-1 C-band SAR scenes collected between 2017 and 2021 were processed using a geocoded SLC processor. Vegetation decorrelation artifacts were mitigated by interpolating the phase observations of Persistent Scatterer (PS) pixels over the densely vegetated Dhaka area. The InSAR surface deformation estimates derived from stacking and Small-Baseline Subset (SBAS) method are consistent with independent GPS time series. A 3 cm/year linear subsidence trend was observed within an area of known groundwater pumping and abundant subsurface clays. Based on analysis with a hydromechanical model for an elastic half-space, the observed subsidence is likely associated with the long-term decline in head. An oscillating seasonal deformation pattern was observed over a much greater region across the study site. Peak subsidence occurred during the monsoon season (September), and peak uplift occurred during the dry season (March). SAR and InSAR observations were used to detect the monsoon flooding extent compared to the dry season. The difference in water load is likely the cause of the seasonal deformation based on an elastic loading model. By identifying and separately modeling the principal controls on deformation, future work can focus on how long-term compaction of aquitards may lead to As mobilization into the adjacent aquifers.

 

 

 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10543

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